It is known that resin films or resin coated papers of low conductivity become electrostatically charged by friction with dielectric materials and/or contact with electrostatically chargeable transport means, e.g. rollers. The charging occurs particularly easily in a relatively dry atmospheric environment.
Sheets, ribbons and webs made of hydrophobic resin or coated with such resin, e.g. a polyester resin or cellulose triacetate, are commonly used as base materials or supports in recording materials. Such supports are subjected to frictional contact with other elements during the manufacture of the recording materials, e.g. during a coating or cutting stage, and during use, e.g. during the recording of information or (in the case of silver halide photographic materials) during image-processing or projection. Especially in the reeling-up or unreeling of dry photographic film in a camera or projector high friction may build up, resulting in electrostatic charges that may attract dust or cause sparking. In unprocessed photographic silver halide emulsion materials sparking causes undesirable exposure marks and degrades the image quality.
In order to reduce electrostatic charging of sheets or webs comprising a hydrophobic resin layer or support without impairing their transparency it is known to apply coatings which are formed of or incorporate ionic compounds such as antistatic high molecular weight watersoluble polymeric compounds having ionic groups at frequent intervals in the polymer chain [ref. e.g.Photographic Emulsion Chemistry, by G. F. Duffin, - The Focal Press - London (1966) - Focal Press Limited, p. 168, and U.S. Pat. No. 4,301,240]. Examples of polymers that have been used for this purpose include salts of polyacrylic acid, of polystyrene sulphonic acid and copolymers which contain quaternary ammonium groups. However, watersoluble antistatic substances ingredients will not remain when the treated sheet or web materials are subjected to an aqueous treatment as is common e.g. in the processing of photographic silver halide emulsion materials.
Thus, watersoluble ionic polymers containing protonated or quaternized amino groups, although providing a good antistatic character before aqueous processing will not offer a satisfactory electrical conductivity for preventing electrostatic dust-attraction of a dried resin film support of a wet-processed photographic silver halide emulsion material since said polymers are leached out from the coated material in the aqueous processing.
In U.S. Pat. No. 4,301,240 a photographic material is described wherein for the purpose of improving mechanical and electrostatic properties a cross-linked acrylic or methacrylic polymer salt is used in dispersed form in a hydrophilic colloid layer binder layer such as a gelatin containing layer of a photographic gelatin-silver halide emulsion layer material.
In U.S. Pat. No. 4,677,050 still other carboxylate containing cross-linked copolymers as defined by their general formula (I) are added in dispersed form in water to hydrophilic coating compositions of photographic silver halide emulsion materials to improve their antistatic character.
The advantages of the use of said dispersed polymeric carboxylate salts, follow from their resistance to diffusion, low swelling power and their property of not influencing the viscosity of gelatinous coating compositions. The dispersed cross-linked polymeric carboxylate salts remain by their insolubility resistant to diffusion in hydrophilic colloid layers under conditions of pH encountered in photographic processing liquids for treating imagewise photo-exposed silver halide emulsion layer materials.
It has been found experimentally by us that especially the alkaline metal salts of said cross-linked carboxylate polymers improve the electrical conductivity of a hydrophilic colloid layer but that said conductivity drops markedly in aqueous media having a pH lower than 5. Since particular acid fixing liquids acting simultaneously as stop bath for the alkaline development have a pH below 5, e.g. in the range of 5 to about 4 a remedy for the sudden decrease in conductivity at said lower pH values has to be found.
It has further found experimentally by us that latices on the basis of cross-linked polymers containing quaternary ammonium salt groups after being treated in alkaline aqueous processing liquids have lost much of their conductivity increasing character.